Polishing pad for wafer polishing device, and apparatus and method for manufacturing same

ABSTRACT

The present invention provides a method for manufacturing a polishing pad, the method comprising: a step for manufacturing a non-woven pad; a polyurethane impregnation step for impregnating the non-woven pad with polyurethane; and a surface polishing step for polishing the surface of the non-woven pad impregnated with polyurethane, wherein the polyurethane impregnation step and the surface polishing step are performed such that the density ratio between the surface layer and the inside of the polishing pad is uniform.

TECHNICAL FIELD

Embodiments relate to a wafer polishing apparatus, and more particularlyto a polishing pad used in a wafer polishing apparatus.

BACKGROUND ART

In general, a single-crystal silicon ingot may be grown and manufacturedusing a Czochralski method. This method is a method of meltingpolycrystalline silicon in a crucible in a chamber, soaking a seedcrystal, which is a single crystal, in the melted silicon, and slowingraising the seed crystal so as to be grown as a single-crystal siliconingot (hereinafter referred to as an ingot) having a desired diameter.

A single-crystal silicon wafer manufacturing process includes asingle-crystal growth process of forming an ingot using the abovemethod, a slicing process of slicing the ingot to obtain a thindisc-shaped wafer, an edge grinding process of grinding an edge of thewafer obtained through the slicing process in order to prevent fractureor distortion of the wafer, a lapping process of removing damage due tomechanical machining remaining on the wafer in order to improve flatnessof the wafer, a polishing process of polishing the wafer, and a cleaningprocess of removing a polishing agent and foreign matter from thepolished wafer.

In the wafer polishing process, thereamong, both surfaces of a wafer maybe simultaneously polished using a double side polishing (DSP)apparatus.

FIG. 1 is a perspective view of a general wafer polishing apparatus.

As shown in FIG. 1 , the general wafer polishing apparatus 100 includesan upper surface plate 110, a lower surface plate 120, an upper pad (orupper polishing pad) 130, a lower pad (or lower polishing pad) 140, acarrier 150, a sun gear 160, an internal gear 170, and a central shaft180.

The upper surface plate 110 and the lower surface plate 120 are disposedso as to be rotatable while facing each other.

The upper pad 130 is disposed under the upper surface plate 110, and thelower pad 140 is disposed above the lower surface plate 120. Inside theupper surface plate 110 and the lower surface plate 120, the upper andlower pads 130 and 140 are disposed so as to face each other in order topolish a wafer W.

Each of the upper surface plate 110 and the lower surface plate 120 mayhave a disc shape, and each of the upper and lower pads 130 and 140,which are attached to the upper surface plate 110 and the lower surfaceplate 120, respectively, may also have a disc shape.

The sun gear 160 is installed at an outer circumference of the centralshaft 180, and the internal gear 170 is installed at an outercircumference of the lower surface plate 120. The internal gear 170 maybe rotated in a direction opposite the rotation direction of the sungear 160.

The carrier 150 is disposed between the upper pad 130 and the lower pad140, and may be rotated by rotation of the sun gear 160 and the internalgear 170. In addition, the carrier 150 has an insertion hole, into whichthe wafer W may be inserted, and a slurry hole, through which slurry maybe introduced. The carrier 150 may be formed in the shape of a dischaving a screw formed on an outer circumferential surface thereof.

Teeth formed at an outer circumferential surface of the sun gear 160 andteeth formed at an inner circumferential surface of the internal gear170 are engaged with teeth 152 formed at the outer circumferentialsurface of the carrier 150. When the upper surface plate 110 and thelower surface plate 120 are rotated about the central shaft 180 by adriving source (not shown), therefore, the carrier 150 performs rotationand revolution.

Although not shown, a plurality of slurry supply holes 190, in whichnozzles configured to supply slurry from above the upper surface plate110 are installed, may be formed through the upper surface plate 110.

In the general wafer polishing apparatus 100 having the aboveconstruction, when a wafer W is inserted into and seated in theinsertion hole of the carrier 150 installed between the upper surfaceplate 110 and the lower surface plate 120, friction occurs between thewafer W and the upper and lower pads 130 and 140 attached respectivelyto the upper surface plate 110 and the lower surface plate 120. At thistime, both surfaces of a plurality of the wafers W mounted in thecarriers 150 are polished by slurry supplied inwards from above theupper surface plate 110 and the polishing pads 130 and 140 in a batchfashion. That is, polishing of the wafer W due to friction may beperformed by rotation of the upper pad 130 of the upper surface plate110 and the lower pad 140 of the lower surface plate 120 in oppositedirections.

However, glazing, in which porous surfaces of the polishing pads 130 and140 are changed due to frequent friction between the polishing pads 130and 140 and the wafer W, and surface layers of the polishing pads areclosed by the slurry and polishing by-products, occurs. Such grazingreduces coefficients of friction of the polishing pads 130 and 140,whereby wafer polishing quality is deteriorated.

DISCLOSURE Technical Problem

Embodiments provide a polishing pad for wafer polishing apparatusescapable of preventing glazing during a wafer polishing process, therebyimproving flatness of a wafer, and an apparatus and method formanufacturing the same.

Technical Solution

An embodiment provides a polishing pad manufacturing method including astep of manufacturing non-woven fabric, a polyurethane impregnation stepof impregnating the non-woven fabric with polyurethane, and a surfacefinishing step of finishing the surface of the non-woven fabricimpregnated with the polyurethane, wherein the polyurethane impregnationstep and the surface finishing step are performed such that a densityratio of a surface layer to the interior of a polishing pad is uniform.

The polyurethane impregnation step may include a pretreatment step ofpretreating the non-woven fabric, a first drying step of removingmoisture from the non-woven fabric, an impregnation step of impregnatingthe non-woven fabric with polyurethane, a second drying step of dryingthe polyurethane contained in the non-woven fabric by impregnation, anda pressing process of pressing the non-woven fabric impregnated with thepolyurethane.

In the impregnation step, a polyurethane impregnation process may beperformed at least twice.

The impregnation step may include a first impregnation process ofimpregnating the non-woven fabric with hydrophilic polyurethane and asecond impregnation process of impregnating the non-woven fabric withhydrophobic polyurethane.

In the surface finishing step, buffing may be performed such that adensity ratio of a porous layer containing the polyurethane to a porouslayer containing no polyurethane in the surface layer of the polishingpad is 1:1.

The non-woven fabric may have a thickness of 4 mm to 6 mm, and thethickness of the non-woven fabric removed by the buffing may be 2.5 mmto 3.5 mm.

The polishing pad may have an overall density of 0.44 to 0.55 g/cm³.

Another embodiment provides an apparatus for manufacturing a polishingpad for wafer polishing apparatuses, the apparatus including a non-wovenfabric manufacturing unit configured to manufacture non-woven fabric, apolyurethane impregnation unit configured to impregnate the non-wovenfabric with polyurethane, and a surface finishing unit configured tofinish the surface of the non-woven fabric impregnated with thepolyurethane, wherein the polyurethane impregnation unit includes afirst polyurethane water tank configured to receive hydrophilicpolyurethane and a second polyurethane water tank configured to receivehydrophobic polyurethane for impregnation.

The surface finishing unit may perform buffing such that a density ratioof a porous layer containing the polyurethane to a porous layercontaining no polyurethane in the surface layer of the polishing pad is1:1.

The non-woven fabric may have a thickness of 4 mm to 6 mm, and thethickness of the non-woven fabric removed by the buffing may be 2.5 mmto 3.5 mm.

A further embodiment provides a polishing pad for wafer polishingapparatuses manufactured using the manufacturing method or apparatus

Advantageous Effects

A polishing pad for wafer polishing apparatuses according to anembodiment and an apparatus and method for manufacturing the same havean effect in that density of polyurethane provided on a surface layer ofthe polishing pad by impregnation is equalized, whereby it is possibleto prevent glazing during a wafer polishing process, and therefore it ispossible to improve flatness of a wafer.

In addition, the polishing pad according to the embodiment has an effectin that high roughness of the surface layer of the polishing pad ismaintained, whereby it is possible to inhibit a conventional phenomenonin which a removal rate is reduced due to an increase in pad use time,and therefore the lifespan of the polishing pad is increased.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a general wafer polishing apparatus.

FIG. 2 is a schematic view showing the construction of a wafer polishingpad manufacturing apparatus according to an embodiment.

FIG. 3 is a flowchart showing a wafer polishing pad manufacturing methodaccording to an embodiment.

FIGS. 4 and 5 are process charts showing a process of manufacturing apolishing pad according to the manufacturing method of FIG. 3 .

FIGS. 6A and 6B are sectional views of a polish pad containingpolyurethane before buffing and after buffing.

FIG. 7 is a graph showing densities of a polishing pad according to anexample and a polishing pad according to a comparative example based onthe thickness thereof.

FIG. 8 is CT images showing the fault states of the polishing pads ofFIG. 7 at a thickness of 100 μm.

BEST MODE

Hereinafter, embodiments will be clearly disclosed through thedescription of the embodiments with reference to the accompanyingdrawings. In the following description of the embodiments, it will beunderstood that, when an element, such as a layer (film), a region, apattern, or a structure, is referred to as being “on” or “under” anotherelement, such as a substrate, a layer (film), a region, a pad, or apattern, it can be “directly” on or under another element or can be“indirectly” formed such that an intervening element is also present.Terms such as “on” or “under” are described on the basis of thedrawings.

In the drawings, the size of each element is exaggerated, omitted, orschematically illustrated for convenience of description and clarity. Inaddition, the size of each element does not entirely reflect the actualsize thereof. In addition, the same reference numerals denote the sameelements throughout the description of the drawings. Hereinafter,embodiments will be described with reference to the accompanyingdrawings.

FIG. 2 is a schematic view showing the construction of a wafer polishingpad manufacturing apparatus according to an embodiment, FIG. 3 is aflowchart showing a wafer polishing pad manufacturing method accordingto an embodiment, FIGS. 4 and 5 are process charts showing a process ofmanufacturing a polishing pad according to the manufacturing method ofFIG. 3 , and FIG. 6 is a sectional view of a polish pad containingpolyurethane before buffing (a) and after buffing (b).

As shown in FIG. 2 , the wafer polishing pad manufacturing apparatusaccording to the embodiment may include a non-woven fabric manufacturingunit 1, a polyurethane impregnation unit 2, a surface finishing unit 3,and a tape pasting and cutting unit 4.

Here, each of the units 1, 2, 3, and 4 may be a combination of a seriesof devices, and each of the units 1, 2, 3, and 4 may constitute a singleconnected manufacture route.

The non-woven fabric manufacturing unit 1 includes a series of devicesconfigured to manufacture non-woven fabric, which is a main materialused in the polishing pad. For example, as shown in FIG. 4 , thenon-woven fabric manufacturing unit 1 may include a supply unit 10configured to supply a bundle of fibers C, a pressing unit 20 configuredto press the bundle of fibers C, and a bonding unit 30 and a punchingunit 40 configured to perform a needle punching process.

The polyurethane impregnation unit 2 includes a series of devicesconfigured to impregnate the non-woven fabric with polyurethane in orderto coat the non-woven fabric with polyurethane. For example, as shown inFIG. 4 , the polyurethane impregnation unit 2 may include a pretreatmentwater tank 50, a first drying unit 60, a first polyurethane water tank70, a second polyurethane water tank 80, a second drying unit 100, and apressing roller 110.

The surface finishing unit 3 includes a series of devices configured toremove a surface layer portion from the non-woven fabric impregnatedwith polyurethane. For example, as shown in FIG. 5 , the surfacefinishing unit 3 may include sandpaper 120 for buffing.

The tape pasting and cutting unit 4 includes a series of devicesconfigured to paste a double-sided tape T to one surface of the buffedpolishing pad and to cut the polishing pad in the form of a circularpad.

For example, as shown in FIG. 5 , the tape pasting and cutting unit 4may include a cutter unit 130, a tape pasting unit 140, a pressing unit150, a shape cutting unit 160, and a package inspection unit 170.

Hereinafter, a polishing pad manufacturing method using the waferpolishing pad manufacturing apparatus according to the embodimentincluding the above construction will be described in detail.

As shown in FIG. 3 , a polishing pad for wafer polishing apparatuses(hereinafter referred to as a polishing pad) according to an embodimentmay be manufactured using a polishing pad manufacturing method includinga non-woven fabric manufacturing step (S100), a polyurethaneimpregnation step (S200), a surface finishing step (S300), a tapepasting and cutting step (S400), and a polishing pad mounting step(S500).

1) Non-Woven Fabric Manufacturing Step (S100)

The polishing pad according to this embodiment starts to be manufacturedin the form of a pad while the non-woven fabric manufacturing step isperformed. The non-woven fabric is fabric that is not woven using aloom. Since fibers are directly combined in the form of fabric, thenon-woven fabric is also called bonded fabric. Here, polyester, viscoserayon, nylon, polypropylene, cotton, hemp, wool, asbestos, glass fibers,or acetate may be selected as the fibers.

The non-woven fabric is manufactured using a dry-laid non-woven fabricmanufacturing method, which does not use water, or a wet-laid non-wovenfabric manufacturing method, which uses water. In the non-woven fabricmanufacturing step (S100) according to this embodiment, the dry-laidnon-woven fabric manufacturing method may be used.

More specifically, in the non-woven fabric manufacturing step (S100), i)the supply unit 10 supplies a bundle of fibers C to the pressing unit20, ii) the pressing unit 20 presses the supplied bundle of fibers Cinto a web (fibers that are thinly spread) W, and iii) the bonding unit30 and the punching unit 40 punch the web (W) fibers using a needle tomanufacture non-woven fabric F, as shown in FIG. 4 (1). The polyurethaneimpregnation step (S200) is performed to provide the manufacturednon-woven fabric F with physical properties necessary for the polishingpad Pad.

2) Polyurethane Impregnation Step (S200)

The polyurethane impregnation step (S200) includes a process of soakingthe non-woven fabric F manufactured in step 1) (S100) in thepolyurethane water tank 70 so as to be impregnated with polyurethane fora predetermined time. A plurality of pores, i.e. a porous layer, ispresent not only at the surface of the non-woven fabric F but also inthe interior of the non-woven fabric F. Polyurethane PU may permeate theporous layer of the non-woven fabric F to provide physical propertiesnecessary for the polishing pad Pad.

Polyurethane PU is a compound generated as the result of combinationbetween polyol and isocyanate. That is, polyurethane is a polymercompound having urethane repeatedly combined in a polymer chain. Thereare epoxy, polyester, and phenol as this compound.

As shown in FIG. 4 (2), the polyurethane impregnation step (S200) mayinclude i) a pretreatment process, ii) a first drying process, iii) animpregnation process, iv) a second drying process, and v) a pressingprocess.

The pretreatment and drying processes are performed before polyurethane(PU) impregnation such that the polyurethane (PU) impregnation processis smoothly performed. The pretreatment process may include a process ofsoaking the non-woven fabric F in the pretreatment water tank 50, inwhich a cleaning solution or a chemical is contained. The non-wovenfabric F manufactured in step 1) (S100) may be moved into thepretreatment water tank 50 by rollers R. After the pretreatment process,the non-woven fabric F may be moved to the first drying process byrollers R.

The first drying process may be a process of removing moisture from thenon-woven fabric F soaked in the cleaning solution or the chemical. Forexample, the first drying process may be performed through the firstdrying unit 60, which is capable of evaporating the cleaning solution orthe chemical using a heater or a fan.

The impregnation process is a process of soaking the non-woven fabric Fin the polyurethane water tank 70, in which polyurethane PU iscontained. Polyurethane PU is manufactured by mixing two or more kindsof liquid, and properties thereof are determined depending on the kindof isocyanate and polyol, which are reactants. Long combinationscontained in polyol assist in forming a soft elastic polymer, andhuge-amount combinations assist in forming a hard polymer. When a lengthcorresponding to an intermediate between two combinations is maintained,high elasticity with moderate stiffness may be achieved. That is, whenpolyurethane PU is manufactured, a ratio between a soft segment and ahard segment, which are components thereof, may be adjusted to acquireelasticity and softness suitable for use. When the percentage of thesoft segment is higher, lower hardness and higher elasticity areachieved.

In the polyurethane (PU) impregnation process, conditions may becontrolled to change the mass, volume, and thickness of polyurethane PUcontained in the non-woven fabric F. Here, the conditions may beimpregnation time, concentration of polyurethane PU, the number ofimpregnations, and the movement speed of the non-woven fabric F.

In this embodiment, density of polyurethane (PU) at the surface and inthe interior of the polishing pad Pad may be equalized, whereby it ispossible to improve air-permeability, and therefore it is possible toremedy glazing. To this end, at least one of the following equalizationconditions may be included in the polyurethane impregnation process.

First, in the polyurethane impregnation process, the non-woven fabric Fcontaining polyurethane PU may be primarily soaked in the secondpolyurethane water tank 80. That is, the polyurethane impregnationprocess may be performed at least twice. In addition, the non-wovenfabric F containing polyurethane PU may be further soaked in a thirdpolyurethane water tank 90 or a cleaning tank 90 so as to be furtherimpregnated with polyurethane or to be cleaned, as needed.

Here, polyurethane in the first polyurethane water tank 70 and thesecond polyurethane water tank 80 may be hydrophobic. That is,polyurethane may not combine with water.

In addition, the first polyurethane water tank 70 may be filled withhydrophilic polyurethane, and the second polyurethane water tank 80 maybe filled with hydrophobic polyurethane. When polyurethane in the firstpolyurethane water tank 70 is hydrophilic, polyurethane may moresmoothly move from the surface to the interior of the non-woven fabric Fwhen the non-woven fabric is impregnated with polyurethane, thanhydrophobic polyurethane.

Second, the non-woven fabric that is impregnated with polyurethane maybe manufactured so as to be thick. For example, the polyurethaneimpregnation step (S200) may be performed on non-woven fabric having athickness of 5 mm manufactured in the non-woven fabric manufacturingstep (S100) (conventional non-woven fabric has a thickness of 2.3 mm).In the surface finishing step (S300), a description of which willfollow, therefore, a buffing thickness may be increased by 2.7 mm morethan the conventional non-woven fabric.

That is, in the embodiment, the non-woven fabric may have a thickness of4 mm to 6 mm, and the thickness of the non-woven fabric that is removedat the time of buffing may be 2.5 mm to 3.5 mm.

Subsequently, the second drying process may be performed. For example,the second drying process may be performed through the second dryingunit 100, which is capable of drying polyurethane using a heater or afan.

Subsequently, the non-woven fabric UF containing polyurethane PU passesthrough the pressing roller 110 so as to be pressed such thatpolyurethane PU deeply permeates even the interior of the non-wovenfabric UF.

3) Surface Finishing Step (S300)

After the polyurethane impregnation step (S200), the surface finishingstep (S300) is performed on the non-woven fabric UF. In the surfacefinishing step (S300), the non-woven fabric UF is sanded or buffed usingsandpaper in order to remove foreign matter from the surface and thebottom of the non-woven fabric UF. Also, in the surface finishing step(S300), the thickness of the polishing pad and the surface porosity ofthe polishing pad may be adjusted.

As shown in FIG. 6(a), the polyurethane (PU) impregnation density of thepolishing pad Pad is high at a surface layer portion of the polishingpad and is gradually lowered toward the interior of the polishing pad.Due to high polyurethane (PU) density at the surface of the polishingpad Pad, therefore, slurry introduced into the surface of the polishingpad Pad at the time of wafer polishing is not moved to the interior ofthe polishing pad. As a result, glazing occurs in the state in which theslurry is adhered to the surface of the polishing pad.

In order to solve this problem, in the surface finishing step (S300),pores P in the surface layer may be further exposed by removing a partof the surface through buffing using the sandpaper 120, as shown inFIGS. 5 (3) and 6(b). Consequently, a ratio of the part of the surfacelayer portion of the polishing pad Pad impregnated with polyurethane PUto the interior of the polishing pad impregnated with no polyurethanemay be increased, whereby the slurry may be moved to the interior of thepolishing pad Pad, and therefore the slurry may not be adhered to thesurface of the polishing pad.

The overall density of the polishing pad Pad may be 0.44 to 0.55 g/cm³,the compression rate of the polishing pad Pad may be 1.9 to 2.0%, andthe hardness of the polishing pad Pad may be 88 Asker C. That is, eventhough the polyurethane (PU) impregnation density in the surface layerportion of the polishing pad Pad is adjusted, fundamental physicalproperties necessary for the polishing pad Pad may be satisfied.

4) Tape Pasting and Cutting Step (S400)

The tape pasting and cutting step (S400) is a step of attaching adouble-sided tape T to one surface of the polishing pad UF impregnatedwith polyurethane PU and cutting the polishing pad in the form of acircular pad.

More specifically, in the tape pasting and cutting step (S400), as shownin FIG. 5 (4), i) the cutter unit 130 cuts the polishing pad UFimpregnated with polyurethane PU to a predetermined length, ii) the tapepasting unit 140 pastes a double-sided tape T to one surface of thepolishing pad UF (PSA prepasting), iii) the pressing unit 150 pressesthe double-sided tape T (PAS pasting, Press), iv) the shape cutting unit160 cuts the polishing pad UF having the double-sided tape T pastedthereto by pressing into a predetermined shape (e.g. a circular shapehaving the size of a surface plate), and v) the package inspection unit170 inspects a product and packages the product (inspection, shipping).

5) Polishing Pad Mounting Step (S500)

One surface of the double-sided tape T of the polishing pad UF packagedin the fourth step (S400) is attached to a surface plate of a waferpolishing apparatus, and a wafer polishing process is performed usingslurry.

FIG. 7 is a graph showing densities of a polishing pad according to anexample and a polishing pad according to a comparative example based onthe thickness thereof.

As shown in FIG. 7 , it can be seen that the polishing pad according tothe example, which was manufactured so as to have a uniform polyurethaneimpregnation rate using the above manufacturing apparatus and method,has an average density value irrespective of the thickness of thepolishing pad (from the top to the bottom). In contrast, the polishingpad according to the comparative example has a high density at surfacelayer portions constituting the top and the bottom.

In the conventional polishing pad (comparative example), slurryintroduced into the surface of the pad is not moved to the interior ofthe pad during the polishing process due to high density of the surfacethereof, whereby glazing occurs in the state in which the slurry isadhered to the surface of the polishing pad.

In the polishing pad according to the example, density at the surfaceand the interior of the pad is uniform, and therefore mobility of theslurry to the interior of the polishing pad may be improved.

FIG. 8 is CT images showing the fault states of the polishing pads ofFIG. 7 at a thickness of 100 μm.

It was observed that glazing occurring at the polishing pad according tothe comparative example was formed from the surface to the interior ofthe polishing pad by a depth of 300 μm. That is, the layer thickness ofglazing may be formed from the front of the polishing pad to a depth of300 μm.

As shown in FIG. 8 , it can be seen from the photographed 100 μmthickness layers of the example and the comparative example that thecomparative example has a larger whiter spot (glazing area).

In the polishing pad according to the example, density at the surfaceand the interior of the pad is uniform, whereby slurry is smoothlyintroduced into the interior of the pad, and therefore the glazing areais controlled from the surface layer of the pad to a depth of 100 μm.

In the polishing pad for wafer polishing apparatuses according to theembodiment and the method of manufacturing the same, the density ofpolyurethane exposed from the surface of the polishing pad is equalized,whereby it is possible to prevent glazing during the wafer polishingprocess, and therefore it is possible to improve flatness of the wafer.

Also, in the polishing pad according to the embodiment, high roughnessof the surface layer of the pad is maintained, whereby it is possible toinhibit a conventional phenomenon in which a removal rate is reduced dueto an increase in pad use time. That is, the lifespan of the polishingpad may be increased.

The features, structures, and effects described in the above embodimentsare included in at least one embodiment, but are not limited to only oneembodiment. Furthermore, features, structures, and effects illustratedin each embodiment may be combined or modified in other embodiments bythose skilled in the art to which the embodiments pertain. Therefore, itis to be understood that such combinations and modifications fall withinthe scope of the present disclosure.

INDUSTRIAL APPLICABILITY

Embodiments are applicable to a polishing pad for wafer polishingapparatuses and an apparatus and method for manufacturing the waferpolishing pad.

1. A method of manufacturing a polishing pad for wafer polishingapparatuses, the method comprising: a step of manufacturing non-wovenfabric; a polyurethane impregnation step of impregnating the non-wovenfabric with polyurethane; and a surface finishing step of finishing asurface of the non-woven fabric impregnated with the polyurethane,wherein the polyurethane impregnation step and the surface finishingstep are performed such that a density ratio of a surface layer to aninterior of a polishing pad is uniform.
 2. The method according to claim1, wherein the polyurethane impregnation step comprises: a pretreatmentstep of pretreating the non-woven fabric; a first drying step ofremoving moisture from the non-woven fabric; an impregnation step ofimpregnating the non-woven fabric with polyurethane; a second dryingstep of drying the polyurethane contained in the non-woven fabric byimpregnation; and a pressing process of pressing the non-woven fabricimpregnated with the polyurethane.
 3. The method according to claim 2,wherein, in the impregnation step, a polyurethane impregnation processis performed at least twice.
 4. The method according to claim 3, whereinthe impregnation step comprises: a first impregnation process ofimpregnating the non-woven fabric with hydrophilic polyurethane; and asecond impregnation process of impregnating the non-woven fabric withhydrophobic polyurethane.
 5. The method according to claim 4, whereinbuffing is performed such that a density ratio of a porous layercontaining the polyurethane to a porous layer containing no polyurethanein the surface layer of the polishing pad is 1:1.
 6. The methodaccording to claim 5, wherein the non-woven fabric has a thickness of 4mm to 6 mm, and a thickness of the non-woven fabric removed by thebuffing is 2.5 mm to 3.5 mm.
 7. The method according to claim 6, whereinthe polishing pad has an overall density of 0.44 to 0.55 g/cm³.
 8. Anapparatus for manufacturing a polishing pad for wafer polishingapparatuses, the apparatus comprising: a non-woven fabric manufacturingunit configured to manufacture non-woven fabric; a polyurethaneimpregnation unit configured to impregnate the non-woven fabric withpolyurethane; and a surface finishing unit configured to finish asurface of the non-woven fabric impregnated with the polyurethane,wherein the polyurethane impregnation unit comprises: a firstpolyurethane water tank configured to receive hydrophilic polyurethane;and a second polyurethane water tank configured to receive hydrophobicpolyurethane for impregnation.
 9. The apparatus according to claim 8,wherein the surface finishing unit performs buffing such that a densityratio of a porous layer containing the polyurethane to a porous layercontaining no polyurethane in the surface layer of the polishing pad is1:1.
 10. The apparatus according to claim 9, wherein the non-wovenfabric has a thickness of 4 mm to 6 mm, and a thickness of the non-wovenfabric removed by the buffing is 2.5 mm to 3.5 mm.